Perfume is a key component for a favorable consumer experience with home and personal care products. It is also often the most costly component of the formulation. Typically, most of the fragrance is quickly lost as the product is used because most of the perfume is trapped in the surfactant system. There has been a long-standing need to improve the utilization of perfumes and to design compositions that provide maximum and prolonged impact in use. It is one objective of this invention to develop a means by which products can be developed to provide greater fragrance impact and novel fragrance characteristics in use.
To this end, the applicant has found that perfume activity (e.g., the aroma of the perfume) both in a product (e.g., surfactant containing product) and upon use (e.g., dilution of product in shower) can be correlated to the thermodynamic characteristics of (1) the perfume itself and (2) the formulation in which the perfume is found.
For example, the degree to which a perfume will partition into oil or water (measured by a so-called “partition coefficient” and a reflection of the hydrophobicity of the perfume) and the degree to which the perfume evaporates (measured by “volatility constant” and a reflection of the volatility of the perfume) are two significant characteristics of the perfume which strongly affect the potential perfume “burst” when said product is diluted. By burst is meant an increase in the concentration of perfume in the vapor phase above the solution (i.e., this is often known as perfume headspace) with respect to the undiluted product and composition. The vapor phase can of course vary depending on product, for example, from a small area above a bottle of perfume to an area in a shower stall.
As noted, the perfume burst is affected not only by the perfume properties, but also by properties of the formulation in which the perfume is found. Thus, the number and type of surfactant micelles found in a surfactant solution also has an effect. For example, in a surfactant with high critical micellization concentration (CMC) (in compositions of high CMC, micelles do not form as readily) perfume “burst” would occur more readily and less dilution is required. The critical micellization concentration is defined as the surfactant concentration at which micelles begin to form from unassociated surfactant monomers (M. J. Rosen, Surfactants and Interfacial Phenomena, 2nd Ed., 1989). Conversely, in a surfactant with low critical micelle concentration (e.g., one where micelles do form easily or, stated differently, don't break apart as readily once formed), a perfume, being generally more hydrophobic, tends to stay in the surfactant more readily. As a result, the perfume will tend not to “burst” (increase perfume headspace) as readily and, to achieve more headspace, more dilution may be required.
Other important formulation factors which may affect the “burst” of the perfume may include, but are not limited to, perfume content in solution and surfactant to water ratio.
Still another factor which can affect perfume “burst” is the environment in which it is found, e.g., such environmental factors as (1) overall sample amount; (2) vapor volume and (3) temperature.
According to the subject invention, applicants have succeeded in putting together a thermodynamic model which can be used to select the types of perfume and formulations which should be used in order to maximize this perfume burst or actual headspace (actual concentration of perfume in vapor phase) when a formulation (e.g., personal wash or shampoo formulation) is diluted in use.
More specifically, applicants have defined a perfume burst index which defines compositions which can deliver a perfume burst upon dilution of at least a certain amount relative to undiluted composition; and further allows applicants to define a process for obtaining such compositions.
In general, the burst is achieved by diluting a surfactant system (e.g., an aqueous surfactant system) where burst begins upon dilution and maximum burst is obtained upon reaching CMC, therefore, releasing all of the perfume from the surfactant system. Thus, a composition yielding a maximum fragrance burst of 20% means the perfume concentration in the headspace increases by about 20% relative to the undiluted product when the solution is diluted through the CMC. The CMC is the point where perfume-surfactant-water system changes to perfume-water system (i.e., system is too dilute for micelles to form).
A surfactant system is defined as a surfactant and/or surfactant mixtures which may include ingredients selected to manipulate the CMC in a continuous phase. These selected ingredients can include urea; glycerine; C1-C12 straight-chained or branched alcohols or diols; water soluble polymers such as polyvinylpyrolidone, polyvinylalcohol, polyethyleneglycol, polypropyleneglycol; multivalent electrolytes such as magnesium, calcium and aluminum salts; and sugars such as dextrose, glucose, maltose, galactose, sucrose. The continuous phase is typically water, but may also include C1-C8 straight-chained or branched alcohols or diols, glycerine, C1-C8 esters and combinations thereof.
Generally, surfactants which may be used include, for example, anionic, nonionic, amphoteric/zwitterionic, and cationic surfactants as discussed in more detail below.
The subject invention relates to a process for preparing or selecting a composition having a fragrance burst, as measured by a “perfume burst index”, of about 20% relative to a composition containing surfactant systems and perfume/fragrance prior to dilution of said product.
More specifically, the invention relates to a process for preparing specific compositions by selecting perfume and/or perfumes and surfactant systems and/or mixtures of surfactant systems and calculating therefrom a perfume burst index (PBI) according to the following formula:   PBI  =            ϕ      -              1.4        /        CMC              K  wherein                φ=the oil/water partition coefficient of selected perfumes or perfumes components in a mixture;        CMC=critical micellization concentration of surfactant systems or mixture of surfactant systems (wt./wt.);        K=volatility constant of perfume or perfume components in a mixture from the continuous phase (atmospheres); and        
The perfumes and surfactant systems are specifically selected to ensure that the PBI calculated is greater than about 3.
It should be understood that the PBI defines the maximum potential fragrance burst which is achieved at the CMC for the surfactant or surfactant mixture. For example, a relatively low PBI (e.g., about 3) will obtain a “burst” of at least 20% as noted. However, if the PBI is higher, much higher fragrance burst can be expected. Thus, for example, a burst of 20% may be achieved upon immediate dilution (assuming high enough PBI) and may continue to 700% or 800% or more at CMC (which as noted is point of maximum potential burst).
As far as applicants are aware, there is no art which specifically discloses that such burst can be obtained with such compositions or which discloses a way of predicting when and under what circumstances such fragrance “burst” will occur based on the dilution behavior of a perfume-surfactant-water system. Further no art of which applicants are aware discloses how such compositions are in turn related, for example, to properties of the perfume (e.g., partition coefficient, volatility) as well as to properties of the formulation (e.g., surfactant concentration and surfactant CMC).